Induction heated device



Feb 18 1947 SHAW 5 853 INDUC'T'ION HEATED DEVI 0;

Filed Jan. 10, 1945 2 Sheets-Sheet 1 IN V EN TOR.

Feb, 1 1 v H. N. SHAW 2,415,853

INDUCTION HEATED DEVICE Filed Jan. 10, 1945 2 Shets-Sheet? Patented Feb. 1%, 1947 UNllED STATES PATENT OFFICE INDUCTION HEATED DEVICE Harold N. Shaw, Erie, Pa.

Application January 10, 1945, Serial No. 572,167

Claims. 1

This invention relates to improvements in induction heated devices.

The invention relates more particularly to induction heated containers of the type illustrated and disclosed in my prior Patents Nos, 1.501005, 1,739,617 and 2,001,219. In these patents a container, suitable for cooking or other purposes, is heated by means of heavy current which flows around a secondary ring or extension cast integral with the container bottom. The secondary extension ring is supported within a ring-shaped groove in the primary unit. In this type of construction the current flowing through the secondary extension reacts with the current flow ing through the primary coil to cause a force which undesirably pushes upwardly on the utensil. In my Patent No. 2,001,219 this force is balanced by means of a downward pull exerted on a centering pin by a pull coil which is connected in series with the primary coil. In this patent there is also disclosed iron support pads which are attached to the utensil and which are arranged to exert a downward :pull on the utensil. This downward pull is the result of a magnetic field which i produced by the secondary current.

The use of a center pull coil adds considerably to the cost of the device, and the use of iron support pads attached to the utensil, without a pull coil, would not create a sufficiently strong downward pull to balance the upward forces which are exerted in the use of high power utensils.

It is a general object of the present invention to provide an induction heated device wherein magnetic pull down members are connected to the laminated ring which embraces the primary coil, the said magnetic pull down members being so designed'as to exert a sufficient downward force to just balance the upward force upon the utensil.

A further object of the invention is to provide in an induction heated device, as above described, practical and efficient means for rigidly securing the magnetic pull down members to the laminated ring after the primary coil is in position.

A still further object of the invention is to provide in a device of the class described means whereby the magnetic pull down members may be of laminated construction so that the pull down force exerted by said members is in phase with the force acting upwardly on the utensil.

A further object of the invention is to provide a construction as above described, and including magnetic pull down pads, wherein the strength of the magnetic field in said pads is controlled by means of an air gap. v

A further object of the invention is to provide an induction heated device wherein the magnetic pull down pads are arranged to bridge dependingextensions of the armature members.

A still further object of the invention is to provide pull down mechanism ,for induction heated devices wherein the pull down mechanism is 10-. cated between theprimary coil and thesecondary ring, and wherein the magnetic field in the pull down mechanism is produced by current flowing in the secondary circuit. I 7

With the above and other objects in view, the invention consists of the improved induction heated device, and all its .parts and combinations, as set forth in the claims and all equivalents thereof. 7 I

In the accompanyingdrawings illustrating one complete embodiment of the preferred form of the invention,- in which the same reference numerals designate-the same parts in all of the views:

Fig. 1 is a verticalsectional view through the device, the upper part of the container being broken away;

Fig. 2 is a top view of the primary unit, part being broken away;

Fig. 3 is a fragmentaryperspective view of the laminated ring which embraces the primary coil;

Fig. 4 is a fragmentary sectional view taken approximately on the line 4-4 of Fig. 1 with the secondary ring removed and with the primary coil omitted; 1

Fig. 5 is a perspective view of a part of one of the pull down pad assemblies including the supporting saddles;

Fig. 6 is a perspective view of a fragment of the bottom of I the container showing the secondary ring and armature arrangement; and

Fig. 7 is a sectional view taken on the line 'l-'! of Fig. 6.

Referring more particularly to the drawings, the device illustrated shows the invention as applied to the heating of a container The container or utensil i9 is; preferably formed of cast aluminum, but other metals may be used. In the form of the invention illustrated there is an annular extension or secondary ring H, as well as a centering ring or post I2 cast integral with the bottom and depending therefrom. A plurality of armature members l3 are cast in the ring in spaced relationship, as illustrated in Figs. 1, 6 and 7. Each armature comprises a plurality of juxtaposed laminations, and each lamination comprises a strip of suitable material, such as electrical steel cut to I-shape, as shown in Fig.6. The armature laminations' are' originally assembled in ring-shaped form with the several armature sections connected to each other by welding at the top while the armatures are held in a suitable jig. The ring of armatures is therefore formed in the exact size to fit the unit before it is cast into the secondary ring ll of the utensil. When the armature members are in position, as illustrated in Figs. 1, 6 and '7, they are separated from each other by wedge-shaped portions It and the wedge-shaped portions are in turn connected by bottom bridging portions l5. The portions I4 and I5 form parts of the secondary ring and are integral with the bottom of the utensil in the preferred form of the invention. If the utensil is formed of sheet metal, then the secondary ring I l and centering ring l2 may be brazed or otherwise secured thereto. In such case the complete secondary ring would be made up as a rigid cast, brazed or welded unit with the top side presenting a surface suitable for efiicient heat conduction to the utensil.

The inside surface of the centering ring I 2 may be reamed to insure that it is exactly concentric with the armature ring. The bottom of the armature ring may be machined'flat to insure a'uniform air gap between the armature ends it and the magnetic pads for purposes to be hereinafter described.

The base is formed principally of a plurality of U-shaped punchings l'l, arranged in circular form, as shown in Figs. 1 and 2. In View of the fact that the inner circumference of the ring is small compared to the outer circumference, extra I punchings 8 are inserted between the outer legs of the U punchings. These U and I punchings are welded to a steel rim l9, and the inner periphery of the U punchings are welded to a steel ring 20 and to a centering post plate 2|, carrying a centering post 22 which fits within the centering ring l2 on the utensil bottom. The welding is done in a suitable jig to provide an accurate laminated ring, designated generally by the numeral 23, which clears the armature ring under all working conditions, hot or cold, while maintaining the smallest clearances which are practical so that there are very short air gaps 24 between the laminations and the ends of the a rmatures 13. By maintaining these air gaps short, the magnetizing current is kept desirably low and power factor high. During the formation of the laminated ring 23, means'must be provided in the welding jig to insure that the centering post 22 is exactly concentric with ring 23 so that the utensil is properly centered when it is in the operative position of Fig. 1.

A suitable lprimary coil 25 is embraced by the U punchings FL The primary coil is suitably insulated, preferably by sheet asbestos, glass fiber, or mica on the top and bottom, and by an insulating powder on the sides. The insulation is designated generally by the numeral 25. The powder and sheet insulation are soaked with oil or varnish and then baked to form a solid mass suitable for conducting heat from the primary coil to the laminations Ill. The top of the primary coil is protected, between the pull down pads, to be later described, by thin cover members 26, which are held in place by mean of turned up edges which snap beneath shoulders 21 on the laminations H, a is clear from the right hand side of Fig. 1. These snap covers 26, as well as the centering post plate 2i, are preferably formed of stainless steel to prevent corrosion.

During the process of assembling the laminated ring'23, the welding jig is provided with suitable means for spacing the laminations so as to provide slots 28 at suitable intervals for a purpose to be hereinafter described.

The entire top of the laminated ring 23 is ground flat, as is clear from Fig. 3, to clean up the welds and to .provide a smooth surface for polishing. The laminated ring 23 forms a core for the primary coil.

The important feature of the present invention resides in the use of the magnetic pull down pad assemblies 29. A fragment of one of these assemblies, disconnected from the unit, is illustrated in Fig. 5. Each assembly includes a plurality of spaced U-shaped supporting saddles 30, formed of non-magnetic steel. By using this material the carrying away of magnetic flux from the U laminations H to the laminations of the pull. down pad assemblies 29 is prevented. Secured between each pair of saddles 30 and forming the working parts of the assemblies 29 are magnetic steel laminated pads 3!. The laminations 3| are not of continuous'length across the saddles 3i), but are broken to provide air gaps 32. the strength of the magnetic field.

Referring to Fig. 2, in which two of the magnetic pull down pad assemblies 29 are illustrated, it is to be noted that each assembly includes a non-magnetic steel pad 33. Each pad projects above the adjacent laminations approximately /64 of an inch to provide a gap 34. In Fig. 1, for purposes of clarity, this gap is exaggerated in size. Actually, however, it is substantially less than the side gaps M. It is preferred to utilize three of the magnetic pad assemblies spaced apart. When these assemblies are in position, the utensil it is supported on the three non-magnetic pads 33. Thus, there is a definite air gap 36 above the laminations 3| of the magnetic pull down pad assemblies 29, and this air gap separates these laminations from the ends ll; of the armature laminations.

Inasmuch as current flowing in the secondary ring I! produces a magnetic field, and inasmuch as this current is very heavy, it would saturate a solid piece of iron bridging the extensions 16 of the armature members l3. This would cause too strong a pull and would result in excessive noise. By having the air gap 32, the downward pullexerted by the laminations 3| of the pull down assemblies 29 can be reduced to just the amount required to balance the forces acting upwardly on the utensil during operation of the device. However, if only the gap 34 were used for this purpose, it would have to be large and might be equal to the gaps A. In such a case the primary coil would produce just as strong a magnetic field through the laminated pads 3| as would the secondary circuit. Inasmuch as the former field in the magnetic pad assemblies 29 would not pass through the gap 34, it would exert no force on the utensil and serve no useful purpose. Instead it would saturate the pads 3! and lower the power factor of the device. Any magnetic flux or field which flows between the primary coil and the secondary circuit is objectionable as it lowers the power factor by inducing voltage on the primary coil but not on the secondary.

A small gap 34 which is much smaller than the gaps A is necessary between the ends I6 of the armatures i3 and the laminated pads 3i to prevent chattering, but this gap must be kept as small as possible in order to prevent flux leakage, as explained above. By utilizing, the spaces or gaps 32 intermediate the pads 3|, the flux is lim- The size of these air gaps determines ea e-3 ited to an amount just enough to balance the forces acting upwardly on the utensil during operation of the device. Either too much or too little force from the pads El will result in objectionable noise because all forces must be perfectly balanced at every instant in the alternating current cycle to insure quiet operation.

'The parts forming each magnetic pull down assembly 29 are welded together in a suitable jig by two Welds 35, as indicated in Fig. 1. These welds secure the laminations forming the magnetic pull down pads 3!, as well as the support-. ing pads 33, to the saddle member 36.

. The-upwardly projecting ends of uhe saddle members 3d are inserted in the slots 28 between laminations of the ring 23 (see Figs. 1, 3 and 4). The upper ends of these saddle members are welded to the laminated ring 23, as at 35. By using a relatively large number of individual saddle members, vibration in the welds across the larhinations and between the saddles is prevented. The Welds 35 are ground fiat.

Solid pieces of iron might be used in place of the laminated magnetic pads 3! but would be more noisy than the latter because the current induced in the solid iron would throw the pull of the pads out of phase with the forces acting to push upwardly on the utensil. Thus a desired balance of these two forces would not be obtained.

By welding the saddles to the primary unit at the upper ends of the saddles, the welds are located far enough away from the primary coil .44 to prevent damage during the welding operation.

The faces of the U laminations laminations forming the armatures i3, which faces provide the main air gaps 2d, are tapered slightly, as shown in Fig. l, to allow for easy removal of the utensil. The cooperating faces of the centering pin 22 and centering ring i:

are tapered for the same reason. The U laminations are cut back below the shoulders 2". so that there is ample clearance A from the ends of the laminations of the magnetic pull down pads 3!.

Pairs of L-shaped supporting saddles might be used in place of the U saddles, but means would have to be provided, such as a non-magnetic weld to hold the two halves of each of the pads 31 apart at the central gaps 32. In use of the device for cooking articles in the utensil I9 or for heating material in the container, with the primary coil connected toa source of electrical supply, an induced current is created within the secondary ring H of the'utensil bottom. This is caused by the magnetic flux which travels from one leg of the laminated ring I1, across one of the air gaps 24 through the armature members l3, across the other air gap 24 and back to the other leg of the laminated ring 23. This current flowing through the secondary ring or extension ll of the utensil creates the desired heat for cooking or other purposes. The current flowing inthe secondary ring [1, however, reacts with the current flowing through the primary coil to cause a force pushing upwardly on the utensil l9. However, this current produces a magnetic flux which travels from one side of the magnetic pull down pads 3| across the air gap 34 into one of the extensions is of the armatures l3, through the armatures l3, downwardly through the other legs [6 of the armatures, downwardly across the air gap 34 to the other ide of the magnetic pull down pad. assembly. This magnetic field causes the magnetic pads 31 toxr't at sundown force which i! and the exactly balances the upward forces acting on the utensil bottom.

It isthus apparent that the magnetic pull down assemblies provide means located between the primary coil 25 and the secondary ring H, operable to hold said ring down against upward forces created by the primary coil. The pull down forces are created by using a magnetic field which is produced by current flowing in the secondary circuit.

Various changes and modifications may be made without departing from the spirit of the invention, and all of such changes are contemplated as may come within the scope of the claims.

What is claimed as the invention is:

1. In an induction heated device, a primary coil connectable with a source of electricity, a member to be heated having an extension forming a secondary circuit removably positionable adjacent said primary coil, means adjacent the primary coil and secondary circuit forming a magnetic circuit, and magnetic means located between the top of the primary coil and adjacent face of the secondary circuit extension for balancing the upward thrust of the primary coil on said extension.

2. In an induction heated device, a primal; coil connectable with a source of electricity, a member to be heated having an extension forming a secondary circuit removably positionable adjacent said primary coil, means adjacent the primary coil and secondary circuit forming a magnetic circuit, and magnetic means located between the top of the primary coil and bottom face of the secondary circuit extension for balancing the upward thrust of the primary coil on said extension, the magnetic field in said magnetic means being produced by current in said secondary circuit only.

3. In an induction heated device, a primary coil connectable with. a source of electricity, a member to be heated having an extension forming a secondary circuit removably positionable adjacent said primary coil, means adjacent the primary coil and secondary circuit forming a magnetic circuit, and magnetic means located between the top of the primary coil and bottom face of the secondary circuit extension for balancing the upward thrust of the primary coil on said extension, there bein an air gap in said magnetic means located below the secondary extension for reducing the strength of the magnetic field to a pre-determined value.

4. In an induction heated device, a primary coil connectable with a source of electricity, a

member to be heated forming a secondary circuit having a surface removably positionable in juxtaposed position with relation to a surface of said primary coil, means adjacent the primary coil and secondary circuit forming a magnetic circuit, and means including magnetic pads sandwiched between the juxtaposed surfaces of the primary coil and secondary circuit for balancing the upward thrust of the primary coil on said secondary circuit member.

5. In an induction heated device, a primary coil connectable with a source of electricity, a member to be heated having an extension forming a secondary cirduit having a surface removably positionable in juxtaposed position with relation to a surface of said primary coil, means adjacent the primary coil and secondary circuit forming a magnetic circuit, and means including laminated magnetic pads sandwiched between the juxtaposed surfaces of the primary coil and I secondary circuit extension for balancing the upward thrust of the primary coil on said extension.

6. In an induction heated device, a .primary coil connectable with a source of electricity, a core member having spaced legs between which said primary coil is positioned, a member to be heated having an extension forming a secondary circuit removably positionable between said legs of said core and over said primary coil, means in said extension forming a magnetic circuit together with said core, and magnetic means located between said core legs and between the primary coil and secondary circuit extension for balancing the upward thrust of the primary coil on said extension.

7. In an induction heated device, a primary coil connectable with a source of electricity, a core member having spaced legs between which said primary coil is positioned, a member to be heated having an extension forming a secondary circuit removably positionable between said legs of said core and over said primary coil, means in said extension forming a magnetic circuit together with said core, magnetic means located between said core legs and between the primary coil and secondary circuit extension for balancing the upward thrust of the primary coil on said extension, and non-magnetic supports for said magnetic means rigidly secured to the latter and to at least one leg of said core.

8. In an induction heated device, a primary coil connectable with a source of electricity, a core member having spaced legs between which said primary coil is positioned, a member to be heated having an extension forming a secondary circuit removably positionable between said legs of said core and over said primary coil, means in said extension forming a magnetic circuit to gether with said core, magnetic means located between said core legs and between the primary coil and secondary circuit extension for balancing the upward thrust of the primary coil on said extension, and U-shaped non-magnetic supporting saddles rigidly secured to said magnetic means and to the legs of said core.

9. In an induction heated device, a primary coil connectable with a source of electricity, a core member having spaced legs between the lower portions of which said primary coil is positioned, the inner faces of said legs having spaced slots, a member to be heated having an extension forming a secondary circuit removably positionable between said faces of the core legs and over saidprimary coil, means in said extension forming a magnetic circuit together with said core, magnetic means located between said core legs and out of contact with the faces thereof, and located between the primary coil and secondary circuit extension for balancing the upward thrust of the primary coil on said extension, and U- shaped non-magnetic supporting saddles rigidly secured to said magnetic means and within the slots of said core legs.

10. In an induction heated device, a primary coil connectable with a source of electricity, a core member having spaced legs between which said primary coil is positioned, a member to be heated having an extension forming a secondary circuit removably positionable between said legs of said core and over said primary coil, armature means in said extension forming a magnetic circuit together with said core, there being air gaps between the ends of said armature .means and the legs of said core, magnetic means 8 including magnetic pads located between said core legs and between the primary coil and secondary circuit extension for balancing the upward thrust of the primary coil on said extension, non-magnetic means for supporting said pads with ends spaced from the legs of the core, and non-magnetic means for supporting the secondary circuit extension with its lower face spaced slightly above the magnetic pads, the

10 field for said magnetic pads passing through the armature means in the secondary circuit extension and through the space between the magnetic pads and said extension.

11. In an induction heated device, a primary coil connectable with a source of electricity, a

core member having spaced legs between which said primary coil is positioned, a member to be heated having an extension forming a secondary circuit removably positionable between said legs of said core and over said primary coil, armature means insaid extension forming a magnetic circuit together with said core, there being air gaps between the ends of said armature means and the legs of said core, and magnetic pads extending transversely between said core legs and located between the primary coil and secondary circuit extension for balancing the upward thrust of the primary coil on said extension, there being a gap intermediate the length of said pads for reducing the strength of the magnetic field to a predetermined value and there being gaps between the ends of said pads and the legs of said core.

12. In an induction heated device, a primary coil connectable with a source of electricity, a

core member having spaced legs between which said primary coil is positioned, a member to be heated having an extension forming a secondary circuit removably positionable between said legs 4.0 of said core and over said primary coil, armature means in said extension forming a magnetic circuit together with said core, there being air gaps between the ends of said armature means and the legs of said core, magnetic pads extending transversely between said core legs and located between the primary coil and secondary circuit extension for balancing the upward thrust of the primary coil on said extension, there being a gap intermediate the length of said pads for reduc- 0 ing the strength of the magnetic field to a predetermined value and there being gaps between the ends of said pads and the legs of said core, and non-magnetic means for supporting the secondary circuit extension so that there is a slight gap between the magnetic pads and the armature means in said extension.

13. In an induction heated device, a ring formed of U-shaped laminations, a primary coil positioned between the legs of said laminations,

a member to be heated having a circular extension removably positionable over said primary coil and between the leg portions of said laminated ring, armature members in said extension f0l'm.. ing a magnetic circuit, together with said laminated ring, spaced magnetic pull down assemblies located at intervals over the primary coi1 and between the legs of the laminated ring and below the secondary circuit extension, each pull down assembly including magnetic pads for balancing the upward thrust of the primary coil on 1 4. In an induction heated device, a primary coil connectable with a source of electricity, a core member having spaced legs between which said primary coil is positioned, a member to be heated having an extension forming a seconda y circuit removably positionable between the legs of said core and over said primary coil, armature members extending transversely in said extension forming a magnetic circuit together with said core, each armature having spaced projections which project downwardly beyond the armature portion therebetween and the material of the secondary extension extending below said intermediate portions of the armatures and being flush at the bottom with the downwardl projecting ends of the armature, magnetic pads extending transversely between said core legs and located between the primary coil and secondary circuit extension for balancing the upward thrust of the primary coil on said extension, and nonmagnetic means for supporting the secondary circuit extension so that there is a slight gap between the downward projections of the armatures and the magnetic pads.

15. In an induction heated device, a primary coil connectable with a source of electricity, a core member having spaced legs between which said primary coil is positioned, a member to be heated having an extension forming a secondary circuit removably positionable between the legs of said core and over said primary coil, ar-

mature members extending transversely in said extension forming a magnetic circuit together with said core, each armature having spaced projections which project downwardly beyond the armature portion therebetween and the material of the secondary extension extending below said intermediate portions of the armatures and being flush at the bottom with the downwardly projecting ends of the armature, magnetic pads extending transversely between said core legs and located between the primary coil and secondary circuit extension for balancing the upward thrust of the primary coil on said extension, there being a gap intermediate the length of said pads for reducing the strength of the magnetic field to a predetermined value and there being gaps between the ends of said pads and the legs of said core, and non-magnetic means for supporting the secondary circuit extension so that there is a slight gap between the downward projections of the armatures and the magnetic pads.

HAROLD N. SHAW.

REFERENCES CITED UNITED STATES PATENTS Name Date Shaw May 14, 1935 Number 

